I have a frame that has a 541mm toptube and a 420mm reach, while the Canyon Roadlite has 542mm and 370mm, they have different ST-angles and I haven`t measured my current bike accurately, but still, is it possible the difference is that big?

aside from the effect of seat tube angle difference, is the head tube angle the same? the top tubes may be near the same length, but do they intersect with the seat tube and head tube at the same height? is the stem height, angle and length the same? are the bars the same?

between all those it'd be easy to end up with way more difference than 50mm

While it's not the traditional approach, I think stack and reach comparisons make it easier. Depending on the manufacturer's geometry ideas you can easy get their 52, 54 and 56 models with essentially the same reach, just different stacks.....

While it might be possible to have that much difference in reach, it is not likely. The 420mm number makes no sense at all. If you look at the charts for most brands, the reach will be far less, even in the largest sizes. The STA only affects the reach by about 1cm per degree and the head tube length only 3mm for each 10mm of head tube difference.

Reach values can easily be misinterpreted because they are only comparable at the SAME stack height. If you're you're comparing 54cm and 56cm frames, for example, the later may have a 20mm taller head tube. You should subtract 6mm from the reach of the smaller frame to bring it up to the same minimum height as the larger frame. The difference in reach will then be 6mm greater than shown in the geometry chart.

Last edited by DaveS on Sat Nov 24, 2012 8:26 pm, edited 1 time in total.

I found an Excel Spreadsheet online on Gearinches that enabled you to plug in various measurements from the geometry and it allowed you to compare frame shapes. Found it useful when buying my Canyon as this said I should go with the 58 to get the same reach as my Planet X where as Canyon's calculator suggested a 56 which would have been too small.

While it's not the traditional approach, I think stack and reach comparisons make it easier. Depending on the manufacturer's geometry ideas you can easy get their 52, 54 and 56 models with essentially the same reach, just different stacks.....

x10000000000

my crux and my sworks sl3 have the same "effective t-t" 537mm from specialized

but the crux has a stack of almost 25mm higher and reach 10mm shorter than the sworks (making it more upright for me, which is fine for cross). Also* angles make a big difference.... same reach even could be affected by steep or less steep seat tube angles. the smaller seat tube angle (and going up higher) u will go further away from the bars.

cervelo has some nerdy power point presentations on stack and reach.

from what i've seen about cervelo and canyon., they both seem to have a similar "style" in taller headtubes (stack) than their other competitors of the same "sizing"

If you're comparing the manufacturer's reach value, then the STA has no relevance at all, in the fit comparison of two frames. Of course steeper STA's require more seatpost setback, or at least require the saddle to be moved further back, to get the same saddle position, relative to the BB.

If two frames have the same reach, but different stacks, then the reach should be corrected to the same stack height on both frames, for a proper reach comparison. You would subtract 3mm of reach for each 10mm of stack height difference, from the reach of the smaller frame.

Of course a smaller frame with less stack could be setup with a lower bar, but most comparisons are made, assuming that the fit is intended to be the same on both frames.

If the STA differs significantly, then apply the formula (cosA-cosB) x saddle rail height to get the difference in the setback required. This calculation is only used for selecting a seatpost, since reach comparisons are not affected by the STA.

Sure. I understand that reach and sta has nothing to do with each other.

But if you ride a 75 degree sta combined with no set-back seatpost or 73 degree sta with a seatpost with lots of setback it'll be difficult for you to get the same position on a 74 degree sta. So sta is something that should be considered when comparing geometries.

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